Starch is the most important calorie source of foods. Staple foods for humans mainly comprise starch and starch-containing foods are widely used, not only as staple foods but also as subsidiary foods or confections. As starch is usually used in the gelatinized form (.alpha.-starch) made by heating in the presence of water, foods containing starch undergo hardening due to retrogradation of gelatinized starch to .beta.'-starch. As a result, palatability and texture of starch-containing foods deteriorate with time, resulting in reduction of commercial value. Therefore, it is difficult to preserve starch-containing foods for a long period fo time or to deliver them over a long distance.
Many attempts have been made in order to prevent or retard deterioration of foods due to retrogradation of starch. Known methods proposed for this purpose include addition of monosaccharides or oligosaccharide, e.g., sorbitol, glucose, sucrose, maltose, etc., which also serve as sweeteners; addition of polysaccharides of the same type as starch, e.g., dextrin, -limit dextrin, starch of glutinous rice or partial hydrolysates thereof, etc.; addition of natural gum or water-soluble polysaccharides, e.g., sodium alginate, etc.; addition of fats and oils or derivatives thereof; addition of surface active agents; and the like. These techniques attained their effects to some extent by taking advantage of the characteristics of the respective additive. However, the preventing of deterioration obtained with prior known additives is still insufficient and there has been a demand for a material free from deterioration or an efficient method of preventing deterioration of foods.